Catechol (amines) and phenols occur as hormones, neurotransmitters, and in proteins. They find use in medicine in the treatment of Parkinsonism, hypertension and cancer. Their side effects include hepatic injury, hemolysis, and photosensitivity. The cytotoxicity of these materials is considered to be related to the production of damaging free radicals and quinones that can occur during their degradation. The aim of this project is to provide information on radical reactions in several such systems, to include identification of radical species and elucidation of their mechanisms of formation and decay to molecular products. Studies of semiquinone and aryloxy radicals from the enzymatic and non-enzymatic degradation of catechol(amine)s and phenols are proposed using both direct and indirect electron spin resonance methods and other appropriate techniques. Specific systems to be investigated are the following: (i) Radical formation from tyrosinase oxidation of catecholamines and anticancer drugs, a reaction which leads to toxic oxidation products and ultimately melanins. (ii) Enzymatic reduction of adrenochrome. Adrenochrome is a toxic oxidation product of epinephrine that can cause myocardial necrosis. (iii) Identification of radicals from the oxidation of tyrosine-containing proteins and polypeptides. (iv) The enzymatic and non-enzymatic oxidation of 4-aminocatechol, a nephrotoxin related to analgesic phenolic drugs with occasional nephrotoxic properties.